sometimes i get this metalic interfearence sound. Restarting the computer usually fixes it but that a pain in the butt.
Is anybody familiar with this sound and how did they or you fix it.
Could it be involved in my tascam digital interface?
and thank you. 
Check Windows Control Panel and make sure that no [u]Windows “enhancements”[/u] are enabled.
Could it be involved in my tascam digital interface?
Could be… I’d say it’s more likely to be a problem on the analog-side, except re-starting Windows wouldn’t affect that. Next time it happens, check the analog output of your interface. It would be helpful if your interface allows hardware monitoring so the sound doesn’t pass-through the computer. (If it has a headphone jack use that, otherwise you can plug your computer speakers directly into the interface.)
My guess is that it’s an initialisation problem in the sound card drivers.
What is your “tascam digital interface”? Is it a USB interface? If it is, then next time it happens, use “Safely remove this device”, then, either power off or unplug the device, then plug it back in again and wait for Windows to reinstall it, then restart Audacity. Does that “fix” the problem without rebooting the computer?